Ferromagnetic materials and methods of preparing the same



United States Patent C) FERRQMAGNETIC MATERHALS AND METHODS (PF PREPARING THE SAME Evert Wiliem Gorter, Eindhoven, Netherlands, assignor,

by mesne assignments, to North American Philips Com.- pany, inc New York, N35! a corporation of Delaware My invention relates to ferromagnetic materials and methods of preparing the same.

In US. Patent 2,762,777, a new class of permanent magnets are disclosed which consist essentially of materials having the composition MFe O in which M is a metal selected from the group consisting of Ba, Sr and Pb and'in which up to 40 atomic percent of one of said metals may be replaced by Ca. These materials are further characterized by a hexagonal crystal structure, namely the crystal structure of the mineral magnetoplumbite.

I have unexpectedly found a closely-related class of compounds having the same crystal structure, but whose composition differs from the aforesaid composition by the replacement of parts of the iron by titanium and cobalt in the crystal lattice. These compounds are decidedly ferromagnetic and are further characterized by permeabilities which are higher than those of the aforesaid materials and often higher than 2 at frequencies of 50 mc./sec. and even much higher frequencies. These materials are also characterized by low losses at those frequencies.

Accordingly, it is a principal object of my invention to provide an entirely new and hitherto unknown class of ferromagnetic materials.

A further object of my invention is to provide a new class of ferromagnetic materials suitable for application at frequencies up to 50 megacycles per second and even higher.

A further object of my invention is to provide a new class of ferromagnetic materials which have high initial permeabilities at frequencies of up to 50 megacycles per second and higher.

A still further object of my invention is to provide a new class of ferromagnetic materials which have low losses at frequencies of up to 50 megacycles and even higher.

These and other objects of my invention will be apparent from the description that follows.

According to my invention I have unexpectedly found that materials having a composition MCO Ti Fe(1 )O19 wherein M is at least one metal selected from the group consisting of barium, strontium and lead and calcium in an amount up to 40 atom percent of said other metals and a has a value from 1.0 to 1.6 have outstanding ferromagnetic properties particularly at high frequencies. I have further found that these materials have particularly good ferromagnetic properties when a has a value of from 1.2 to 1.45. The materials of my invention have a'hexagonal crystal structure equal to that of the mineral magnetoplumbite.

The materials of my invention are characterized by having low losses and high initial permeabilities at high frequencies even at 50 mc./s. and higher.

The materials of my invention may be manufactured by si-ntering at a temperature above 1200 (2., in "an oxidizing atmosphere such as air or oxygen, a finely divided mixture of ferric oxide and the oxides of the other metals necessary to form my materials. In place of the oxides of these metals compounds of these metals which form oxides upon heating such as the acetates, oxalates or carbonates may be used. Alternatively, instead of starting with the simple oxides it is possible to start with previously obtained reaction products of these oxides such as for example BaFe m, and'SrFe O If desired, the finely-divided initial material may be pre-sintered at a comparatively low temperature (about 800 to 1100 C.) in air or oxygen, the reaction product pulverized again and the resultant powder sintered again, which series of treatments may be repeated once more or several times.

Also if desired 'sintering agents such as silicates and fluorides may be added'to the mixture of oxides.

The high-frequency properties of the materials according to the invention may in many cases be considerably improved by ensuring in the manufacture of such materials 'that the size of the individual crystallites does not become excessive. This may be ensured by thoroughly pulveriz'ing the initial material and preventing any undue crystal growth during sintering. Strong crystal growth may be avoided by utilizing a sintering process, which is comparatively moderate, that is to say in most cases cornparatively short. It 'must be regarded as a surprising circumstance that the high-frequency properties of the materials concerned may be improved in the manner indicated.

Small amounts of impurities such as Fe O and compounds which have the spinel structure may be present without adversely affecting the magnetic properties of my materials.

Bodies of desired shape may be formed by sintering the starting mixtures directly in the desired shape. Alternatively bodies of desired shape may be formed by "reg-rinding the sintered material of my invention, or the presintered material, molding the resultant powder into the desired shape and si'ntering the molded product if necessary. A binder such as water, a solution of nitrocellulose or a solution of carboxymethylcellulose may be added to the powdered mixtures before molding if necessary.

In a further embodiment of my invention the finely divided material of my inve'n'tion is molded to form a body of the desired shape by pressing the relative material together with a binding agent which is capable of being hardened (for example a polyester resin or an ethoxyli-n resin), followed byhardening the molded body.

My invention will now be described in greater detail with reference to the following examples and table.

EXAMPLE I 39.8 gs. of barium carbonate (69. 1% by weight of barium), 31.8 gs.'of cobalt carbonate (44.5% by Weight of cobalt), 19.3 gs. of titanium oxide (99.9% by weight of TiO and 156.8 gs. of ferric oxide (99.6% by weight of Fe O were mixed. These amounts are chosen so that in the formula given above a had the value 1.2. This mixture was ground in a rotating ball mill with alcohol for 15 hours. After drying, the mixture was presintered at 1100 'C. for two hours and again ground in the same -manner. Subsequently, the-powder was again ground with alcohol in a vibrating ball mill for 4 hours. A ring was then molded from the powder obtained after drying at a pressure of 1.5 tons/cm. This ring was sin-tered in oxygen by passing it through an oven. The zone of maximum temperature (1280 C.) which had a length of 10 cms. wastravers'ed in 6-minutes.

3 EXAMPLE n 11:1.35

39.8 gs. of barium carbonate, 35.8 gs. of cobalt carboate, 21.6 gs. of titanium oxide and 151.9 gs. of ferric thereof will be readily apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

oxide were ground in the manner indicated in Example 5 Ferromagnetl? material FPnsisfing essehtiany of I presintered and again ground. A ring was molded from mixed crystals having a composition corresponding to the the powder obtained and sintered at 1280 C. (ring A) formula and another ring was molded and sintered at 1350 C. MC; T IV Irr g both in y i in all Oven s ated in EX- wherein M is at least one metal selected from the group ample 1, consisting of barium, strontium, lead and a has a value EXAMPLE III between about 1.0 and 1.6 and having a hexagonal crys- (a=1.45) tal structure isomorphic to that of the mineral magneto- 39.8 gs. of barium carbonate, 38.4 gs. cobalt carbonate, Plumblte, sald mammal having an initial Permeability I 232 titanium Oxide and 1486 of ferric o-Xide of at least 2 and a loss factor, tan 6, of less than about 0.6 were treated similarly as in the previous examples. The at frequencies up to 9 F final sintering process was effected at 1350 C. in oxygen. The fermmagnetlc mammal of dam 1 m Whlch 1n the formula has a value between about 1.2 and 1.45. EXAMPLE I 3. The ferromagnetic material of claim 1 in which M (a=1.6) is barium. 50.1 gs. of barium carbonate, 52.0 gs. of cobalt car h fefl'emagnefie material of Claim 1 in which M bonate, 32.0 gs. of titanium oxide and 179.6 gs. of ferric ls Strontiumoxide were ground in the manner above described and, The ferromagnetic material of Claim 1 in WhichM is after drying, the mixture was presintered at 1050 C. for lead- 2 hours and again ground in a rotating ball mill for 15 The fefromagnetle material of Claim 1 in which the hours A ring was molded f the powder Obtained at metal selected from the group consisting of barium, strona pressure of 1.5 tons/cmF, the ring being sintered for hum, and e is replaced y P to about 0 atom per- 2 hours in a stationary oven at 1320 C. in oxygen and cent of ealelllml l l d i h h oven. A method of manufacturing a ferromagnetic ma- X. examination proved h the rings obtained terial having a high initial permeability, t, and a low loss cording to these examples consisted of crystals with the factor, itan 5 at frequencies p to 50 and higher crystal structure isomorphic to that of the mineral magcomprising the Steps, P p g a n y divided xtur i i of ferric oxide, at least one compound selected from the The magnetic properties of the rings obtained accordgroup Consisting of barium OXide, Strontium Oxide, lead ing to these examples are tabulated in the following table. Oxide and calcium Oxide in an amount Corresponding to In the table 11 corresponds to the term a in the formula P to atom Percent Of calcium for the metals barium, f th compounds of my invention strontium and lead, titanium oxide and cobalt oxide in Th expression 5 may b l i d b h f llo amounts suitable to form a composition corresponding to ing remarks. A magnetic alternating field of a small the formula B. 8. (122B.) 19 wherein M is at amplitude generally produces an almost sinusoidally vary- 4 least one metal Selected from the group consisting of ing inductance in a ferromagnetic body. Due to the elec' barium, Strontium, lead and calcium in an amount P to tro magnetic losses, a phase-difference exists between the 40 atom Percent of Said latte! metals, a has a Value f field strength and the inductance. Consequently, it is from about i0 and sintel'ing Said mixture at a common practice to represent the initial permeability of a temperature of about 1200 C. to about 1350 C. in an ferromagnetic body as a complex value. This is expressed 5 atmosphere Containing at least as much Oxygen as by th l ti p,= ,'--i Thi l ti Shows th th 8. The method of claim 7 in which a portion of the inductance may be regarded as constituted by two comxid s ar f rmed during the sintcring operation. ,ponents, of which one is co-phasal with the field applied 9. The method of claim 7 in which part of the oxides and the other lags by 90 with respect thereto. The value used are replaced by previously reacted products between ,u' is the real portion of the initial permeability and is t or more of h id included in the table The loss factor tan 5 is given by 10. The method of claim 7 in which the finely divided the formula: mixture is presintered at a temperature between about tan 800 C. and 1100 C. before being finally sintered at a This loss factor tan 5" is also referred to as the loss temperature c e 1200 C. factor of the ferromagnetic materials. 11. A method of preparing a ferromagnetic body hav- Table MAGNETIC PROPERTIES It low 831nc./s. 145 m '../s. 275 1110.15. 500 mcJs. Example 11 frequency It tanb tan 5 p. tan 6 n tans As can be readily observed from the foregoing table the initial permeability ,0 of the ferromagnetic bodies of my invention remain at high levels even at frequencies of 275 mc./s. and above and the loss factor tan 5 remains at a relatively low value even at high frequencies.

While I have described my invention in connection with specific embodiments and applications, other modifications ing'a high initial permeability, ,u', and a low loss factor, tan 6 at frequencies up to 50 mc./s. and higher comprising the steps, preparing a finely divided mixture of ferric oxide, at least one compound selected from the group consisting of barium oxide, strontium oxide, lead oxide and calcium oxide in an amount corresponding to up to 40 atom percent of calcium for the metals barium, strontium and lead, titanium oxide and cobalt oxide in amounts suitable to form a composition corresponding to the formula MCo Ti Fe O wherein M is at least one metal selected from the group consisting of barium, strontium, lead and calcium in an amount up to 40 atom percent of said latter metals, a has a value of from about 1.0 to 1.6; molding said mixture into a body of desired shape and sintering said body at a temperature of about 1200 C. to 1350 C. in an atmosphere containing at least as much oxygen as air.

12. A method of preparing a ferromagnetic body having a high initial permeability, and a low loss factor, tan 5, at frequencies up to 50 mc./ s. and higher comprising the steps, preparing a finely divided mixture of ferric oxide, at least one compound selected from the group consisting of barium oxide, strontium oxide, lead oxide and calcium oxide in an amount corresponding to up to 40 atom percent of calcium for the metals barium, strontium and lead, titanium oxide and cobalt oxide in amounts suitable to form a composition corresponding to the formula MCo Ti Fe O wherein M is at least one metal selected from the group consisting of barium, strontium, lead and calcium in an amount up to 40 atom percent of said latter metals, a has a value of from about 6 1.0 to 1.6; pre-sintering said mixture at a temperature between about 800 C. and 1100 C., regrinding the sintered material, molding said regrinded material into a body of desired shape and sintering said body at a temperature of about 1200 C. to about 1350 C. in an atmosphere containing at least as much oxygen as air.

References Cited in the file of this patent UNITED STATES PATENTS OTHER REFERENCES Romeijn: Philips Research Reports, vol. 8, p. 330, October 1953.

Gorter: Philips Research Reports, vol. 9, pp. 403-418, December 1954.

Phillips Technical Review, vol. 18, No. 6, pp. -154. 

1. FERROMAGNET MATERIAL CONSISTING ESSENTIALLY OF MIXED CRYSTAL HAVING A COMPOSITION CORRESPONDING TO THE FORMULA 